1. Field of the Invention
The invention relates to plasma-deposited silicon compound thin film dielectric materials produced in high frequency glow discharges. Thin film capacitors using such dielectric materials have an improved dissipation factor (tan .delta.) and a reduced tendency to age rapidly.
2. Description of Prior Art
The capacitance C of a parallel electrode condenser filled with a dielectric medium is given by the formula: EQU C=(.epsilon..sub.o K'A/d)
where
.epsilon..sub.o is the permittivity of free space, PA1 K' is the relative permittivity of the dielectric, PA1 A and d are the area and spacing of the electrodes, respectively.
Since C varies inversely with the thickness d of the dielectric, it is evidently advantageous to make the latter as thin as possible. In the case of most conventional solid dielectrics, a lower limit of thinness is imposed by the appearance of excessive numbers of voids and other defects in the dielectric which render it unsatisfactory below this lower limit. Plasma (or glow discharge) polymers, and other plasma-deposited thin films, constitute a class of synthetic insulating materials which can be prepared practically free of such defects. Consequently, it is felt that they hold promise as dielectrics for thin film capacitors.
However, as reported in: "Electrical Properties of Plasma-Polymerized Thin Organic Films," Plasma Chemistry and Plasma Processing, Vol. 3, No. 3, 1983, Gazicki and Yasuda, a summary of the electrical properties of such dielectric materials, there are indications that such promise has not been realized for two reasons: the dissipation factor (tan .delta.) of the polymerized dielectrics is generally much poorer than for conventional polymers; and there is a greater tendency for the polymerized dielectrics to age rapidly as compared to conventional polymers. The former is illustrated at Table I, page 282 of the reference.
It has now been surprisingly and unexpectedly found that the characteristics of plasma deposited thin films can be improved by carrying out the deposition on a substrate at elevated temperatures.
Teachings relating to microwave plasma-polymerization of organo-silicones using a heated substrate are found in: Polymerization of Organosilicones in Microwave Discharges. II. Heated Substrates, J. Macromol. Sci.-Chem., A15(2), pp. 197-213 (1981), Wrobel et al; Advances in Basic and Applied Aspects of Microwave Plasma Polymerization, Thin Solid Films, 115 (1984), pps. 109-124, Wertheimer et al, and Optical Properties of Plasma-Polymerized Organosilicone Films, Canadian Journal of Physics, Volume 60, Number 5, 1982, pps. 628-631, Wertheimer et al. The first disclosure of certain limited aspects of the invention herein was reported in the Conference Record of the 1984 IEEE International Symposium on Electrical Insulation, Montreal, June 11-13, 1984 at pages 167 to 170, Ramu et al.